1. Field of the Invention
The present invention relates to an X-ray diffraction apparatus making it possible to execute in-plane diffraction measurement.
2. Description of the Related Art
The in-plane diffraction measurement, as shown in FIG. 1A, designates a measuring technique in that an X-ray 12 is incident on a sample surface 10 at a grazing incident angle α (a very small incident angle of about 0.1° to 0.5°, for example) and a diffracted X-ray 14 is detected at an outgoing angle β grazing from the sample surface 10. A circle 16 indicated by an imaginary line denotes a plane including the sample surface 10. The in-plane diffraction is a phenomenon in which an X-ray is diffracted on a crystal lattice surface substantially perpendicular to the sample surface. Since the diffracted X-ray is detected within a plane substantially flush with the plane 16 including the sample surface 10, this technique is called as in-plane. When the in-plane diffraction measurement is employed, crystal information only in the vicinity of the sample surface is obtained, so that the in-plane diffraction measurement is especially used in analyses of a thin film sample.
On the other hand, in the general case in which an X-ray diffraction is generally measured using an X-ray diffractometer, as shown in FIG. 1B, the diffracted X-ray 14 is detected within a plane 20 including both the normal line 18 of the sample surface 10 and the incident X-ray 12. Such a general measuring technique will be called as, in this specification, out-of-plane diffraction measurement against the in-plane diffraction measurement. Thinking about measurement of a thin film sample with the out-of-plane diffraction measurement, it also requires that an X-ray 12 is incident on the sample surface 10 at a grazing incident angle α for reducing the effect of a substrate under the thin film. Accordingly, the out-of-plane diffraction measurement of the thin film sample would become a so-called asymmetrical X-ray diffraction measurement in that a diffraction pattern is measured with the fixed incident angle α relative to the sample surface 10. In this case, an optical system to be used is not for a focusing method but for a parallel beam method.
The in-plane diffraction measurement requires a dedicated apparatus different from a general X-ray diffraction apparatus. There is a desire, however, that both the in-plane and the out-of-plane diffraction measurement can be made with the use of a common X-ray diffraction apparatus. An X-ray diffraction apparatus satisfying the desire is known as disclosed in Japanese Patent Publication No. 11-304731 A (1999). The procedure of the in-plane diffraction measurement of a thin film sample using this prior-art apparatus is as follows: the sample surface is get upright; an X-ray detector is arranged to turn around a horizontal axis of rotation (i.e., turn in a vertical plane); an X-ray which travels horizontally is incident on the sample surface at a grazing angle; and the X-ray detector is rotated in a vertical plane so as to detect an in-plane diffracted X-ray from the sample surface.
On the other hand, the procedure of X-ray diffraction measurement with a θ–2θ scan (i.e., the out-of-plane diffraction measurement) using the same apparatus is as follows: the sample surface is get upright in the same way as in the in-plane diffraction measurement; the X-ray detector is arranged to turn around a vertical axis of rotation (i.e., turn in the horizontal plane) different from the in-plane diffraction measurement; the sample is rotated around the vertical axis of rotation by an angle θ relative to an incident X-ray which travels horizontally; and the X-ray detector is rotated around the same axis of rotation as the θ rotation by an angle 2θ so as to detect a diffracted X-ray from the sample surface. If a thin film sample is to be measured with the out-of-plane diffraction measurement using this X-ray diffraction apparatus, another procedure is also effective in that a diffracted X-ray is measured using the parallel beam in which an X-ray is incident on the sample surface at a grazing angle and only the X-ray detector is rotated around the vertical axis of rotation.
If the above-mentioned known X-ray diffraction apparatus is used, both the out-of-plane diffraction measurement and the in-plane diffraction measurement can be made for a thin film sample, in principle. In the out-of-plane diffraction measurement, the X-ray detector is rotated within a horizontal plane, and such rotation of the X-ray detector is achieved with the conventional goniometer, enabling the angular control to be performed with a high degree of accuracy. Accordingly, the resolution of the detected diffraction angle is superior. On the other hand, in the in-plane diffraction measurement, the same X-ray detector must be rotated within a vertical plane, so that it is difficult to have the high-accuracy angular control because of the rotation against the gravitation. Even if the high accuracy rotation is achieved within the vertical plane, the rotational control mechanism would become expensive for the rotation of the X-ray detector with a high degree of accuracy within both the horizontal plane and the vertical plane.